The answer to this question is not intended to be disrespectful, but the best description I can give for a recommended mixer type is what is called a mortar mixer. Typical mortar mixers are either a horizontal trough with a rotating blade or an angled rotating drum.  Mortar mixers come in different sizes and are made by several different manufacturers.  Some pictures are attached.
 
Mortar mixers are a subset of solids mixers, designed for wet solids.